Automotive instrument panels and door panels are typically composites which are made of a rigid backing which supports a semi-rigid urethane foam with the semi-rigid urethane foam being covered with a skin compound. Such skin compounds are typically blends of polyvinyl chloride (PVC) with ABS (acrylonitrile/butadiene/styrene polymers) which are sometimes modified with nitrile rubber (NBR). The nitrile rubber is included in such blends as a permanent modifier for the PVC which provides it with a higher degree of flexibility.
The automotive industry is currently moving toward more aerodynamic body designs which typically include larger glass areas. Such design changes have significantly increased the heat and ultraviolet light aging requirements of automotive interiors. This has in turn significantly increased the demands put upon the polymers which are utilized as skins in automotive interior panels.
Heat and light stabilizers can be employed to improve the heat and ultraviolet light aging characteristics of conventional PVC/ABS/NBR blends which are utilized as skins for automotive interior panels. However, the degree to which the aging characteristics of such blends can be improved by the addition of additives is limited. In fact, there is a demand for performance characteristics in such applications which heretofore has not been realized by the utilization of heat and light stabilizers. For instance, it would be highly desirable for the skins used in automotive panels to resist discoloration and cracking under conditions of high heat and intense ultraviolet light throughout the life of the vehicle.
NBR/ABS/PVC blends offer an array of physical properties which make them useful as a skin composition for automotive panels. The NBR acts as a permanent flexibilizing monomer for the PVC. It also acts as a shrinkage control agent, and embossing aid, and improves grain retention. The NBR in such blends further provides vacuum forming gauge control and exhibits low fog characteristics. NBR is highly compatible with PVC and has the capability of being recycled.
U.S. Pat. No. 5,380,785, U.S. Pat. No. 5,415,940, U.S. Pat. No. 5,504,155, U.S. Pat. No. 5,504,160 and U.S. Pat. No. 5,616,651 disclose a rubbery polymer which can be blended with PVC to make leathery compositions. These compositions are particularly useful in manufacturing skins for automotive interior panelling. Skin compositions which are made utilizing this rubbery polymer provide a higher level of resistance to heat and ultraviolet light than those made utilizing conventional NBR/ABS/PVC blends. The rubbery polymers disclosed by these patents also offer low fog characteristics, low odor, shrinkage control and grain retention. They also act as an embossing aid and as a permanent flexibilizing modifier. However, one drawback to these rubbery polymer/polyvinyl chloride blends is that they contain a halogen.
There is currently a demand for skin compositions having excellent heat and ultra-violet light resistance that do not contain halogens, such as polyvinyl chloride. This is because industry in general and the automotive industry in particular are attempting to reduce the amount of halogenated materials in industrial products for improved recyclability and other environmental reasons.